A spectator reaction plane detector for the LHC

The ability to determine the reaction plane of a heavy ion collision using spectator neutrons is key to the study of directed flow and the chiral magnetic effect (CME) in these reactions. A shower max detector, known here as the Spectator Reaction Plane Detector (SRPD) has been developed to map spectator neutron positions at zero degrees. In this specific design the SRPD is positioned between two elements of a Zero Degree Calorimeter (ZDC). The SRPD is comprised of a 4 x 4 array of 2 x 2 x 1 cm quartz elements. GEANT simulations of detector performance will be compared to SPS Pb ion test beam results. Predictions from GEANT for full energy LHC Pb beams will be presented.